Arrested development in human hookworm infections: an adaptation to a seasonally unfavorable external environment.

Contrary to general belief, larvae of Ancylostoma duodenale do not always develop directly to adulthood upon invasion of man. In West Bengal, India, arrested development appears to be a seasonal phenomenon which results in (i) reduction of egg output wasted in seeding an inhospitable environment and (ii) a marked increase in eggs entering the environment just before the monsoon begins.